Eosinophilic granuloma of bone as a component of the syndrome histiocytosis X is discussed with respect to clinical, pathologic, and radiologic diagnostic biases and discrepancies employing illustrative case material. The subject is reviewed in historical perspective selectively, with emphasis on those features that may serve as a valuable resource in evaluating initial patient presentations and subsequent follow-up evaluation. Salient pathologic and pathogenetic considerations especially germane to clinical phenomena are reviewed, and current therapeutic modalities are summarized.